Imagine Frank Lobdell, Richard Diebenkorn, Elmer Bischoff and David Park — who created a veritable Mount Rushmore of Bay Area art — sharing a bottle of wine and a casual dinner at a cafe, before repairing to one of their studios for a weekly drawing session with a nude model.

That group, which did indeed meet weekly from 1959 to 1965, eventually broke up. But a reconstituted circle, whose members included Lobdell and Nathan Oliveira, resumed regular figure drawing sessions in the late 1960s and ’70s. An extraordinary body of figurative work emerged from the gatherings, which permitted Lobdell and others to experiment free from the glare of critical appraisal.

Although never intended for public scrutiny, more than 50 of Lobdell’s drawings — mostly nudes dating from two periods in his career (1963-1968 and 1972-1974), done in wash, ink, graphite, crayon and gouache — are now part of the revelatory exhibition “Frank Lobdell Figurative Drawings,” which opened last week at Stanford’s Cantor Arts Center and continues through Feb. 21.

Lobdell, who lives in Palo Alto and taught art at Stanford for more than 25 years before his retirement in 1991, is primarily known as an abstract expressionist painter, influenced by Clyfford Still and Mark Rothko. But his drawings, with their contrasting warm and cool tones, proved to be a remarkable laboratory for developing a vocabulary of shape, light and shadow.

Dashing off two or three from a single pose and rarely signing or reworking them after completion, these studies — exercises really — are essentially excerpts from the private notebooks of an accomplished artist that illuminate the inner workings of a creative mind.

“Figure drawing is still at the core of a lot of artists’ work — that’s the history of art,” says Hilarie Faberman, the Cantor Center’s Halperin Curator of Modern and Contemporary Art. “Frank produced very serious, beautiful work for 50 years. It’s work that comes out of Goya, out of Rembrandt, out of Picasso.

“There’s a real sensibility in how he chooses to pose his nudes, how he represents them, what they are or aren’t wearing, what’s highlighted, what’s in the middle of the visual field, These (choices) are very different for Frank than they are for Bischoff or Diebenkorn.” (To enable visitors to compare the artists’ approaches, the show juxtaposes Lobdell’s drawings with several by Diebenkorn, Bischoff and Oliveira.)

What’s inescapable about Lobdell’s erotically charged, if not directly sexual, naked female forms — some partially clothed, others arranged in languid, frank or provocative positions — is their overt sensuality. In “Figure Drawing No. 90, 1964,” a naked woman crawls across an unmade bed; “No. 78, 1965,” an otherwise breezy summer idyll, features a sunbathing woman, naked except for a floppy hat, propping herself up on her elbows as her nipples jut forward like projectiles.

Some drawings are more demure, like the seated figure in a chair found in “No. 5, 1964.” A side of view of a woman with her face resting in her hand, framed by dark stripes on the back of the chair behind her, the drawing betrays a sophisticated understanding of light. Then, there’s the cool, moody and modern “No. 12, 1973,” an ink and ink-wash of a woman seated on the floor, absorbed in reading a book, a bluish-gray light grazing her breast and arms.

Many of the bodies are contorted, set in impossible, tortured poses, lower limbs folded at a harsh 90-degree angle to torsos as in “No. 25, 1967. The twisted, cross-legged, seated figure of “No. 5, 1973” has a cloud of darkness swirling around her neck and head; and an enigmatic woman curled on her side in “No. 13, 1974” is partially shrouded in darkness and lit by shafts of light as if alternately bathed by seawater and sun.

The giant ghost of Picasso and that artist’s convoluted, attraction-repulsion dynamic with women loom large here. “No. 17, 1974,” with its sharp, unrelenting angles, recalls him, as do the fragmented body parts of “No. 1, 1967.” In it, a woman awash in blackness, except for the white of her breasts and thighs, is pictured upside down, her feet at the top of the drawing, with a smudge for a mouth and slashes for eyes.

“Frank Lobdell’s nudes are loose women “… not literally but figuratively,” observes Robert Flynn Johnson in his insightful catalog essay. “They flow across beds on which they are posed; spill out of the chairs in which they lounge. He juxtaposes the curves of hips, breasts, and buttocks against the geometry of furniture.

“The starkness of flesh is achieved through the use of the untouched or lightly washed paper against the dark-washed background interiors. There is an unabashed sensuality and spirit to these women. The eroticism comes in part because they are not depicted as individuals but as a universal female presence “… natural, alluring, and somewhat dangerous.”

But how does one identify the true source of that “danger”?

The idea of a group of collegial, middle-aged men, warmed by wine and food, spending the evening drawing a naked model or two holding hellish poses conjures a disturbing image of its own. There are more than enough crotch shots, aimed right at the eye level, to alert a team of therapists.

“Frank’s drawings are in your face the way his paintings are, with exploded limbs and heads,” she says. “It’s really tough, very powerful stuff. I’m not a psychoanalyst, but I think there’s a lot of violence and anger. I don’t know if it’s directed at women or at humanity, but a lot things get blown apart.

“Maybe it’s a reaction to what he saw in the war, how he was raised. He’s a man who has been married three times. I can’t really say, but there’s certainly a lot going on there.”